The long-term, overall objective of this research is to advance our understanding of the structural basis of glomerular filtration, and especially to advance our understanding of the structural basis for the abnormal glomerular filtration found in various glomerular diseases. Emphasis in this research will be placed on the glomerular basement membrane since the evidence currently available indicates that it is the main size and charge barrier in the glomerulus which retains plasma proteins in the circulation and prevents their passage into the urine. The specific problems to be studied are: (1) the chemical nature of the known structural components of the GBM; (2) the role played by each of the structural components of the GBM in filtration and attachment under normal and pathologic conditions; (3) the nature and distribution of the various GBM components in glomerular diseases associated with proteinuria; (4) the cellular source -- i.e., whether endothelial, epithelial, or mesangial -- of the individual GBM components; and (5) the role of each of the glomerular cell types in the filtration process and in the production, maintenance and turnover of the GBM. These problems will be investigated in both in vivo and in vitro systems (kidney slices, isolated glomeruli) using normal animals and those with various experimentally-induced glomerular disease (e.g., rats with aminonucleoside-nephrosis or serum sickness nephritis; NZB/NZW or diabetic mutant mice). The approach used to investigate these problems will involve a combination of techniques including, high resolution transmission and scanning electron microscopy, cell fractionation, enzyme digestion, enzyme cytochemistry, radiolabeling and autoradiography, immunocytochemistry, column chromatography, and polyacrylamide gel electrophoresis.